In patients with known or suspected liver disease, obtaining a biopsy sample is often indicated. Liver samples may be obtained by a variety of techniques.1-4 Surgical biopsy allows the whole liver to be visually inspected and palpated, providing an ideal opportunity to obtain biopsy samples of focal lesions for histologic examination, culture and antimicrobial sensitivity testing, and metal analysis. Surgical biopsy also provides a larger tissue sample for a more complete histologic review and allows the veterinarian to examine the biopsy site for adequate hemostasis.2 This article features guidance on when and how to perform a surgical hepatic biopsy.

INDICATIONS

The indications for performing a liver biopsy include substantially or persistently increased liver enzyme activities or serum bile acid concentrations, hepatic hyperbilirubinemia, generalized changes in hepatic ultrasonographic echogenicity, unexplained hepatomegaly, or the presence of solitary or multiple focal lesions within the hepatic parenchyma.1 Liver biopsy is particularly important when the results of biochemical testing and advanced imaging modalities such as ultrasonography or scintigraphy are not adequate to establish a diagnosis. Additionally, histologic information can be combined with an already determined diagnosis to tailor specific treatment protocols, evaluate the response to therapy, and determine the prognosis. Specific indications for a surgical biopsy include microhepatia, a hepatic abscess or cyst, or a lesion that is difficult to localize on ultrasonographic examination.1 In addition, excisional biopsy of a pedunculated or solitary mass may provide treatment opportunities.

SELECTING AND COMPARING LIVER BIOPSY METHODS

Liver samples may be obtained percutaneously by blind or ultrasound-guided biopsy or surgically by laparoscopy or celiotomy.1-4 Selecting the appropriate method is determined by the size of the liver, the type and size of the lesion, and the patient's size and overall health.1,2

Biopsy samples from unstable patients or from patients with severe coagulopathy are best obtained by percutaneous means such as fine-needle aspiration or Tru-Cut biopsy, particularly if diffuse disease is suspected.1 However, both of these methods are significantly inferior to wedge biopsy, potentially affecting an accurate diagnosis.5-8 Cytologic examination of samples obtained by fine-needle aspiration cannot provide information about tissue architecture and may be nondiagnostic for lesions that exfoliate poorly. The correlation between cytologic examination of fine-needle liver aspirates and histologic examination of hepatic biopsy samples is poor; diagnostic correlation of samples was 30% in dogs and 51% in cats in one study and 29% in multiple species in another study.5,6 In fact, cytologic and histologic examinations have a significantly lower correlation in hepatic tissue than all other tissues studied, including cutaneous, subcutaneous, nasal, osseous, lymphatic, splenic, gastrointestinal, cerebral, and ocular tissues.6

Sample size and quality are also variable when ultrasound-guided tissue core biopsy samples are obtained. In one study, only 77% of intended liver biopsies retrieved hepatic tissue, and 22% of the samples were less than 2 mm long and lacked appropriate lobular architecture.7 Thirteen percent of the samples were completely devoid of tissue, and another 10% contained skeletal muscle, blood, or small intestine. Only 60% of samples obtained by Tru-Cut biopsy were of diagnostic quality.7

In another study, samples obtained with 18-ga spring-triggered biopsy needles using ultrasound guidance or direct observation during laparotomy or immediately postmortem had one-third to one-fourth of the median surface area of those obtained with wedge biopsy.8 Because of this small sample size, a diagnosis based on needle biopsy correlated with that of wedge biopsy in less than half the patients. Additionally, the severity of pathology was graded as significantly less in needle biopsy samples for most morphologic parameters, with the exception of inflammation, which was graded more severe as compared with wedge samples. Smaller needle biopsy samples were unable to achieve the necessary number of portal triads per sample to provide an accurate diagnosis of portal triad diseases such as portal venous hypoplasia or portal atresia and were subject to misinterpretation by evaluators.8 Laparoscopic biopsy allows better visualization of the site compared with ultrasonography but may provide less tissue volume compared with a surgical wedge biopsy.